What color thread would you use?

This is my first quilt. My daughter designed it so of
course it will be her quilt. I am going to hand quilt it. The backing is black. Should I use coordinating color threads in the blocks ie: black on black blocks, white on white blocks, red on red blocks or would you use a contrasting color? What color would you use?
(I hope the picture attached.)

I'll be curious to see what others say, but my initial thought is all white. That way the back will have a very pretty pattern that will show up. If you do the stitch in the ditch, it won't show much on top. You did a great job, and I love the pattern and colors.

I personally love varigated thread. Why go to all the trouble of handquilting if you are going to try and hide your work. I may be very old fashioned but it is not a quilt in my eyes until it is quilted.